Water-soluble single-wall carbon nanotubes as a platform technology for biomedical applications

ABSTRACT

The present invention provides for novel methods of generating phenyl sulfonated single-wall carbon nanotubes (1), particularly wherein such phenyl sulfonated single-wall carbon nanotubes can be dissolved in water as true solutions and provide a platform for a variety of biomedical applications.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application for Patent claims priority to U.S. Provisional Patent Application Ser. No. 60/714,484; filed Sep. 6, 2005.

TECHNICAL FIELD

This invention relates generally to carbon nanotube materials, and specifically to methods of derivatizing single-wall carbon nanotubes with species that render them water soluble.

BACKGROUND INFORMATION

Single-walled carbon nanotubes (SWNTs) are a tubular crystalline arrangement of carbon with anisotropic dimensions (approximately 1 nm diameter, with variable length). Although carbon nanotubes have an enormous potential in biotechnology, SWNTs have not yet been developed for medical applications. This is primarily due to the lack of chemistries that are needed to establish true solubility of well-characterized SWNTs. Current chemical methods for water suspended SWNTs require harsh sonochemical treatments in order to effectively disperse nanotubes. However, these methods are currently incapable of conferring thermodynamically stable water-based dissolutions of carbon structures since surfacted SWNT solutions are simply metastable colloidal suspensions, where they transiently individualize but always reaggregate over time since this is their thermodynamically favorable state. Therefore, true water soluble nanotube solutions are those solutions that entropically favor individualized nanotubes. Phenyl sulfonated SWNTs are true water soluble carbon nanotubes and can serve as a platform technology for the development of SWNTs for several industries including pharmaceutical, energy, and electronics.

BRIEF DESCRIPTION OF THE INVENTION

The present invention provides for novel methods of generating phenyl sulfonated single-wall carbon nanotubes, particularly wherein such phenyl sulfonated single-wall carbon nanotubes can be dissvolved in water as true solutions and provide a platform for a variety of biomedical applications.

In some embodiments, the present invention is directed to a method comprising the steps of: (a) providing a plurality of phenylated SWNTs, wherein said phenylated SWNTs comprise a plurality of phenyl groups covalently bonded to the sidewalls of the SWNTs; and (b) reacting said phenylated SWNTs with sulfuric acid to yield phenyl sulfonated SWNTs comprising SWNTs with sulfonated phenyl groups covalently bound to their sidewalls. In some such methods, the phenylated SWNTs are made by a method comprising the steps of: (a) providing a plurality of SWNTs; and (b) reacting said SWNTs with benzoyl peroxide. In some or other embodiments, the phenylated SWNTs are made by a method comprising the steps of: (a) providing a plurality of SWNTs in liquid ammonia; (b) reducing said SWNTs with an alkali metal to yield reduced SWNTs; and (c) reacting said reduced SWNTs with an aryl halide. In some of these latter embodiments, the aryl halide is selected from the group consisting of chlorobenzene, bromobenzene, iodobenzene, and combinations thereof.

In some of the above-described embodiments, there further comprises a step of purifying the phenyl sulfonated SWNTs. In some embodiments, there further comprises a step of dispersing the phenyl sulfonated SWNTs in an aqueous-based solvent.

In some embodiments, the methods of the present invention may be applicable to other small diameter (<3 nm) carbon nanotubes (CNTs), where such nanotubes may comprise two or more walls.

The foregoing has outlined rather broadly the features of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Applicants have synthesized stable, truly water-soluble, phenyl sulfonated SWNTs. Phenyl sulfonated SWNTs can serve as the basis for numerous applications in the development of SWNTs for a wide variety of industries (e.g. energy, pharmaceutical, and electronics). These SWNT formulations have demonstrated remarkable water solubility (>500 mg/L), and in vitro biocompatibility testing has shown well-tolerated response in several cell lines.

There are several potential uses for carbon nanotubes that could impact biotechnology and clinical applications. For example, the monitoring of specific biological markers for cellular pathology is of significant clinical importance in order to coordinate cellular targeted therapeutics to improve health.

Phenyl sulfonated SWNTs can be used as molecular scaffolds for the attachment of cell specific diagnostic agents by attaching targeting molecules (e.g., antibodies, peptides) to the phenyl groups of the SWNT. These synthetic biocompatible nanoscale carriers can be used for targeted intracellular and extracellular contrast and drug delivery. Phenyl sulfonated endohedral nanotubes encapsulated with chemical contrast agents (e.g., gadolinium or iodine) can simultaneously shield the body from these toxic substances yet still allow for the safe administration of these materials for applications in diagnostic imaging systems such as magnetic resonance imaging (MRI) or computed tomography (CT).

The present invention provides a major advantage over existing methods that can be currently found in literature. All current water solutions of carbon nanotubes involve metastable suspensions that over time re-aggregate to either precipitate and/or form bundled suspensions. The significant advantage of the current invention is that phenyl sulfonation confers a state of true water solubility, individualized, de-bundled, and which keeps the SWNTs in it's disaggregated and individualized condition. This is evidenced by cryoTEM images.

Methods of Making Phenyl-Sulfonated SWNTs

Phenylated SWNTs are sulfonated by reaction of phenylated SWNTs with sulfuric acid (H₂SO₄), wherein —SO₃H substitutes for —H on the phenyl groups at a position para to their attachment to the SWNT. Typically this is done by simply dispersing the phenylated SWNTs in oleum.

Applicants herein describe two primary methods for the synthesis of phenylated SWNTs: (1) Benzoyl peroxide and (2) Birch arylation. Such methods are further described in Ying et al., “Functionalization of Carbon Nanotubes by Free Radicals,” Org. Lett., 5, pp. 1471-1473 (2003); and Liang et al., “A Convenient Route to Functionalized Carbon Nanotubes,” Nano Lett., 4, 1257-1260 (2004).

1. Benzoyl Peroxide

After purification, both SWNTs and benzene are added to a three-necked round bottom flask equipped with a homogenizer. The contents of the flask are then homogenized for 10 min before benzoyl peroxide is added. Next, the mixture is heated under argon at 80° C. for 2 h and homogenized. Contents are allowed to cool and the contents of the flask are diluted with benzene, and filtered over a PTFE membrane (0.2 μm), which is washed extensively with chloroform to produce phenylated SWNTs.

2. Birch Arylation

SWNTs are added to a dried 100 mL three neck round bottom flask. NH₃ is then condensed into the flask followed by the addition of small pieces of alkali metal. Next, 1-iodobenzene is then added and the reaction mixtures are stirred overnight with slow evaporation of NH₃. The flask is then cooled in an ice bath as methanol is added slowly followed by the addition of water. After acidification, the nanotubes are extracted into hexane and washed several times with water. The hexane layer is then filtered through a PTFE membrane (0.2 μm) filter and then washed with ethanol and chloroform.

The following examples are included to demonstrate particular embodiments of the present invention. It should be appreciated by those of skill in the art that the methods disclosed in the examples that follow merely represent exemplary embodiments of the present invention. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments described and still obtain a like or similar result without departing from the spirit and scope of the present invention.

EXAMPLE 1

This Example serves to illustrate the synthesis of SWNT-phenyl-SO₃H (1) and SWNT-phenyl-SO₃Na (2), in accordance with some embodiments of the present invention. Further details of such chemistry can be found in Sayes et al., “Functionalization density dependence of single-walled carbon nanotubes cytotoxicity in vitro,” Toxicology Letters, 161(2), pp. 135-142 (2006).

The SWNTs described in this Example were produced at Rice University by the HiPco process (Bronikowski et al., “Gas-phase production of carbon single-walled nanotubes from carbon monoxide via the HiPco process: A parametric study,” J. Vac. Sci. & Technol. A, 19(4), pp. 1800-1805 (2001)) and purified as described previously (Xu et al., “Controlled multistep purification of single-walled carbon nanotubes,” Nano Lett., 5(1), pp. 163-168 (2005)). SWNTs with residual metal less than 1 wt % were obtained after purification.

Compound 1, comprising a plurality of sulfonated phenyl groups attached to its sidewall, was prepared using a two-step process. First, SWNTs (40 mg, 3.33 mmol of carbon) and benzene (100 mL) were added to a 250 mL three-necked round bottom flask equipped with a homogenizer (Peng et al., “Sidewall functionalization of single-walled carbon nanotubes with organic peroxides,” Chem. Comm., 3, pp. 362-363 (2003); Ying et al., “Functionalization of carbon nanotubes by free radicals,” Organic Letters, 5(9), pp. 1471-1473 (2003)). The contents were homogenized for 10 min before benzoyl peroxide (807 mg, 3.33 mmol for the most functionalized level; 202 mg, 0.833 mmol for the medium-functionalized level; 25 mg, 0.104 mmol for the least functionalized level) was added, and heated under argon at 80° C. for 2 h with homogenizing. After cooling, the contents of the flask were diluted with 100 mL of benzene, filtered over a PTFE membrane (0.2 μm), and washed extensively with chloroform to produce phenylated SWNTs.

In the second step of the above-described two-step process, the phenylated SWNTs (20 mg) were dispersed in oleum (20 mL, H₂SO₄, 20% as free SO₃) and heated to 80° C. for 4 h under an argon atmosphere to produce a suspension of SWNT-phenyl-SO₃H. The suspension was carefully poured into 100 mL of ice water, filtered over a polycarbonate membrane (0.22 μm), and washed extensively with water to produce 1.

Compound 2 was prepared by dispersing 1 (20 mg) in 1M NaOH (30 mL), and heating to 80° C. under argon overnight. The contents were diluted with 100 mL of water, filtered over a polycarbonate membrane (0.22 μm), and washed extensively with water.

EXAMPLE 2

This Example serves to illustrate the characterization of compounds 1 and 2, in accordance with some embodiments of the present invention.

Degree of functionalization was determined both qualitatively using Raman spectroscopy, and quantitatively using thermogravimetric analysis (TGA) and x-ray photoelectron spectroscopy (XPS). Dispersion characteristics, as well as concentrations, were determined with cryo-transmission electron microscopy.

While much of the chemistry described herein has been directed to SWNTs, those of skill in the art will recognize that much of this chemistry may be applicable to other small diameter (<3 nm) carbon nanotubes (CNTs), where such nanotubes may comprise two or more walls. Additionally, other methods of generating phenylated SWNTs (which are subsequently sulfonated) may be employed.

All patents and publications referenced herein are hereby incorporated by reference to an extent not inconsistent herewith. It will be understood that certain of the above-described structures, functions, and operations of the above-described embodiments are not necessary to practice the present invention and are included in the description simply for completeness of an exemplary embodiment or embodiments. In addition, it will be understood that specific structures, functions, and operations set forth in the above-described referenced patents and publications can be practiced in conjunction with the present invention, but they are not essential to its practice. It is therefore to be understood that the invention may be practiced otherwise than as specifically described without actually departing from the spirit and scope of the present invention as defined by the appended claims. 

1. A method comprising the steps of: a) providing a plurality of phenylated SWNTs, wherein said phenylated SWNTs comprise phenyl groups covalently bonded to the sidewalls of the SWNTs; and b) reacting said phenylated SWNTs with sulfuric acid to yield phenyl sulfonated SWNTs (1).
 2. The method of claim 1, wherein the phenylated SWNTs are made by a method comprising the steps of: a) providing a plurality of SWNTs; and b) reacting said SWNTs with benzoyl peroxide.
 3. The method of claim 1, wherein the phenylated SWNTs are made by a method comprising the steps of: a) providing a plurality of SWNTs in liquid ammonia; b) reducing said SWNTs with an alkali metal to yield reduced SWNTs; and c) reacting said reduced SWNTs with an aryl halide.
 4. The method of claim 3, wherein the aryl halide is selected from the group consisting of chlorobenzene, bromobenzene, iodobenzene, and combinations thereof.
 5. The method of claim 1 further comprising a step of purifying the phenyl sulfonated SWNTs.
 6. The method of claim 1 further comprising a step of dispersing the phenyl sulfonated SWNTs in an aqueous-based solvent.
 7. The method of claim 1 further comprising a step of reacting the phenyl sulfonated SWNTs with NaOH to yield SWNT-phenyl-SO₃Na (2).
 8. A method comprising the steps of: a) providing a plurality of phenylated small diameter CNTs (SD-CNTs), wherein said phenylated SD-CNTs comprise phenyl groups covalently bonded to the sidewalls of the SD-CNTs; and b) reacting said phenylated SD-CNTs with sulfuric acid to yield phenyl sulfonated SD-CNTs.
 9. The method of claim 8, wherein the SD-CNTs are selected from the group consisting of single-wall carbon nanotubes, double-wall carbon nanotubes, triple-wall carbon nanotubes, and combinations thereof.
 10. The method of claim 8, wherein the phenylated SD-CNTs are made by a method comprising the steps of: a) providing a plurality of SD-CNTs; and b) reacting said SD-CNTs with benzoyl peroxide.
 11. The method of claim 8, wherein the phenylated SD-CNTs are made by a method comprising the steps of: a) providing a plurality of SD-CNTs in liquid ammonia; b) reducing said SD-CNTs with an alkali metal to yield reduced SD-CNTs; and c) reacting said reduced SD-CNTs with an aryl halide.
 12. The method of claim 11, wherein the aryl halide is selected from the group consisting of chlorobenzene, bromobenzene, iodobenzene, and combinations thereof.
 13. The method of claim 8 further comprising a step of purifying the phenyl sulfonated SD-CNTs.
 14. The method of claim 8 further comprising a step of dispersing the phenyl sulfonated SD-CNTs in an aqueous-based solvent.
 15. The method of claim 8 further comprising a step of reacting the phenyl sulfonated SD-CNTs with NaOH to yield SD-CNT-phenyl-SO₃Na. 